The present invention relates generally to a light beam polarization apparatus, and more particularly to a light beam polarization converter for electro-optical devices, such as liquid crystal projection displays.
With the advent of the information technology (IT) age, there is an increasing demand for various electro-optical displays, such as liquid crystal projection type displays. In this type of display, the light source is not inherently integrated, and thus an external source may be required for image display. As the demand for higher quality displays increases, it is becoming more and more important that the utilization efficiency of light sources be enhanced. A conventional way to increase efficiency is to convert the non-polarized light beams of a light source into linearly polarized light beams having a single polarization state, as disclosed in, for example U.S. Pat. No. 5,122,895 to Takanashi et al., wherein a conventional converter, the so-called P-S converter is disclosed. The P-polarized light component refers to the optical component of the electric field oscillation direction that is parallel to the plane of the incident light beam. The S-polarized light component is the optical component perpendicular to that plane.
As shown in prior art FIG. 1, in a conventional liquid crystal projection type display, the light beam emitted from a light source 10 is projected through a projection lens onto a screen (not shown) through the processing of a parallelizing lens 11, a diffusion plate 12, a P-S converter 13, color-splitting lenses 14 and 15, a reflecting mirror 16 and respective liquid crystal displays 301, 302 and 303. The main function of the P-S converter 13 is to reduce the optical loss of light beams when screened through the liquid crystal elements 301, 302 and 303 for specific polarization.
FIG. 2 shows a schematic perspective view of a conventional P-S converter 70. The non-polarized light beams I emitted from a light source travels upward from the bottom side of the P-S converter 70, and is converted therein and thereby emitted from the top side of the P-S converter 70 as a single S-polarized state light beam.
FIG. 3 shows a typical optical path of a light beam in a conventional P-S converter. One light beam (designated xe2x80x9cI1xe2x80x9d) of a plurality of light beams emanating from the light source is representative. The light beam I1 is incident to the P-S converter through an anti-reflection film 70, and then subsequently becomes a light beam I2 having both P- and S-polarization states. The light beam I2 is then incident on a polarization splitting film 73 with a P-component I4 penetrating through and a S-component I3 being reflected. The P-component I4 is converted by a half-wave plate 78 and further travels through an anti-reflection film 79 as a light beam I6 of a single S-polarization state. The S-component I3 reflected by the splitting film 73 is further reflected by a highly reflective film 75 and then penetrates through an anti-reflection film 77 as a light beam I6 of a single S-polarization state.
Since the effect of polarization conversion described above may not be obtained if the light beam emitted from the light source is incident to the portion 81 as shown in FIG. 3, the conventional P-S converter only achieves efficiency of at best 50% in converting the polarization state of light beams. In addition, the configuration of conventional P-S converters is very complicated and carries relatively high manufacturing costs. It is also known in the art that a display incorporating such a conventional converter is notorious for high power consumption.
In view of the above problems, the principal object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which reduces the optical loss in light beam output, is suitable for mass production, and decreases manufacturing costs.
Another object of the present invention is to provide a light beam polarization converter for converting an illumination source into a single polarization light source, which is easily integrated with conventional devices and achieves highly efficient polarization conversion.
To achieve these objects, the present invention provides a light beam polarization converter for converting an illumination light source having a plurality of polarization states into a polarization light source, comprising
an under plate having undulated lower and upper surfaces in conjugate to each other for converging and parallelizing the light beams respectively;
a substrate having an upper surface and a ridged lower surface disposed on the under plate;
a phase retardation film of high reflectivity disposed partially on the lower surface of the substrate; and
a polarization splitting film disposed on the upper surface of the substrate, providing transmission of predetermined polarization states and reflection of predetermined polarization states of the illumination light source.
Another light beam polarization converter in accordance with the present invention is similar to the converter described above except that the phase retardation film is not included therein, and the lower surface of the substrate functions to proceed total reflection of the light beams, such that the conversion of the polarization states can be achieved.
The present invention further provide a light beam polarization converter for converting an illumination light source having a plurality of polarization states into a polarization light source, comprising
an under plate having undulated lower and upper surfaces in conjugate to each other for converging and parallelizing the light beams respectively;
a substrate having a ridged upper surface and a ridged lower surface disposed on the under plate;
a phase retardation film of high reflectivity disposed partially on the lower surface of the substrate;
an upper cover having a ridged lower surface, substantially complementary to the ridged upper surface of the substrate and facing therewith, and an upper surface; and
a thin film disposed between the upper cover and the substrate, the index of refraction thereof is different from that of the substrate.
Another light beam polarization converter in accordance with the present invention is similar to the converter described above except that the phase retardation film is not included therein, and the lower surface of the substrate functions to proceed total reflection of the light beams, such that the conversion of the polarization states can be achieved.
In order to enhance the optical performance, the ridge pitches between ridges on the upper and lower surfaces of the substrate and on the lower surface of the upper cover may be constant or not, and the direction of the polarized light beams reflected by the polarization splitting film or by the thin film and the upper cover should not be parallel to that of the ridge lines on the upper surface of the substrate, thus allowing greater freedom of converter design. Moreover, the undulations, such as cylindrical, spherical or non-spherical undulations, on the upper and lower surfaces of the under plate should be corresponding to each other in a conjugate way to ensure the light beams passing through in parallel, and thus enhance the transmitting efficiency of light beams passing through the converter. The ridged lower surface of the substrate is designed for total reflection of the light beams so as to proceed or even further enhance the conversion of the polarization states of the light beams.